From 2828466e23e0fb443ce20805e4c1b963261092e7 Mon Sep 17 00:00:00 2001
From: Luke Else <mail@luke-else.co.uk>
Date: Wed, 16 Mar 2022 22:31:54 +0000
Subject: [PATCH] Insert Method added to Doubly Linked list

---
 C#/Datastructures/DoublyLinkedList.cs | 38 ++++++++++++++++++++-------
 C#/Datastructures/LinkedList.cs       |  1 +
 C#/Program.cs                         | 34 +++++++++++++-----------
 3 files changed, 48 insertions(+), 25 deletions(-)

diff --git a/C#/Datastructures/DoublyLinkedList.cs b/C#/Datastructures/DoublyLinkedList.cs
index 1c1bcfa..b93eae9 100644
--- a/C#/Datastructures/DoublyLinkedList.cs
+++ b/C#/Datastructures/DoublyLinkedList.cs
@@ -23,7 +23,7 @@ namespace C_.Datastructures
             //Create a new Class with a single item
             return new DoublyLinkedList<T>()
             {
-                Head = DoublyLinkedListNode<T>.Create(value, null, null),
+                Head = DoublyLinkedListNode<T>.Create(value, default, default),
                 Count = 1
             };
         }
@@ -36,10 +36,10 @@ namespace C_.Datastructures
             DoublyLinkedList<T> list;
 
             list = list1;
-            if (list == null || list.Count == 0) return list2;
+            if (list == default || list.Count == 0) return list2;
 
             //Find end of list and append fist item of next list
-            if (list2 == null || list.Count == 0) return list;
+            if (list2 == default || list.Count == 0) return list;
 
             DoublyLinkedListNode<T>? end = list.Traverse();
 
@@ -61,7 +61,7 @@ namespace C_.Datastructures
 
                 //Return Value
                 DoublyLinkedListNode<T>? node = Traverse(i);
-                if (node != null) return node.Value;
+                if (node != default) return node.Value;
                 return default;
             }
             set
@@ -74,22 +74,42 @@ namespace C_.Datastructures
                 node!.Value = value;
             }
         }
-        public void Add(T value)
+        public void Append(T value)
         {
             Count++;
 
             if (Tail != null && Count > 0)
             {
-                Tail.Next = new DoublyLinkedListNode<T> { Value = value, Next = null, Prev = Tail };
+                Tail.Next = new DoublyLinkedListNode<T> { Value = value, Next = default, Prev = Tail };
                 Tail = Tail.Next;
                 return;
             }
 
-            Head = new DoublyLinkedListNode<T> { Value = value, Next = null, Prev = null };
+            Head = new DoublyLinkedListNode<T> { Value = value, Next = default, Prev = default };
             Tail = Head;
             
         }
 
+        public void Insert(int index, T value)
+        {
+            if (index > Count) throw new System.Exception("Error! Index outside of Bounds");
+            
+            //Fetch point in list and add new item
+            DoublyLinkedListNode<T>? node = Traverse(index - 1);
+            node!.Next = new DoublyLinkedListNode<T>{
+                Value = value,
+                Next = node.Next,
+                Prev = node
+            };
+
+            //Create backlink in the list
+            if(node.Next.Next != default)
+                node.Next.Next.Prev = node.Next;
+
+            Count++;
+            
+        }
+
         public bool Delete(int index){
             DoublyLinkedListNode<T>? node = Traverse(index);
 
@@ -153,7 +173,7 @@ namespace C_.Datastructures
         }
         private DoublyLinkedListNode<T>? Next(DoublyLinkedListNode<T> current)
         {
-            if (current != null)
+            if (current != default)
                 return current.Next;
 
             return null;
@@ -161,7 +181,7 @@ namespace C_.Datastructures
 
         private DoublyLinkedListNode<T>? Prev(DoublyLinkedListNode<T> current)
         {
-            if (current != null)
+            if (current != default)
                 return current.Prev;
 
             return null;
diff --git a/C#/Datastructures/LinkedList.cs b/C#/Datastructures/LinkedList.cs
index 36869ca..c9c21ba 100644
--- a/C#/Datastructures/LinkedList.cs
+++ b/C#/Datastructures/LinkedList.cs
@@ -91,6 +91,7 @@ namespace C_.Datastructures
 
             //Fetch point in list at which item will be added
             LinkedListNode<T>? node = Traverse(index - 1);
+
             node!.Next = new LinkedListNode<T> { 
                 Value = value, 
                 Next = node.Next 
diff --git a/C#/Program.cs b/C#/Program.cs
index d75807d..61bc7ed 100644
--- a/C#/Program.cs
+++ b/C#/Program.cs
@@ -7,25 +7,27 @@ Console.WriteLine("Hello, World!");
 
 DoublyLinkedList<int> list = new DoublyLinkedList<int>();
 
-list.Add(1);
-list.Add(2);
-list.Add(3);
-list.Add(4);
-list.Add(5);
-list.Add(6);
-list.Add(7);
-list.Add(8);
+list.Append(1);
+list.Append(2);
+list.Append(3);
+list.Append(4);
+list.Append(5);
+list.Append(6);
+list.Append(7);
+list.Append(8);
 
 DoublyLinkedList<int> list2 = new DoublyLinkedList<int>();
 
-list2.Add(1);
-list2.Add(2);
-list2.Add(3);
-list2.Add(4);
-list2.Add(5);
-list2.Add(6);
-list2.Add(7);
-list2.Add(8);
+list2.Append(1);
+list2.Append(2);
+list2.Append(3);
+list2.Append(4);
+list2.Append(5);
+list2.Append(6);
+list2.Append(7);
+list2.Append(8);
+
+list.Insert(9, 5);
 
 list.Delete(2);